1. Field of the Invention
The present invention relates to an uplink radio resource allocation method for allocating, at a radio base station, an uplink radio resource used for uplink user data transmission to a mobile station, a radio base station and a radio network controller.
2. Description of the Related Art
In a general mobile communication system, between one of radio base stations Node B (refer to FIG. 1A) arranged in a cellular pattern and a mobile station UE, user data is transmitted through a radio communication link.
Here, as shown in FIG. 1B, a radio communication link used for transmitting user data from the radio base station Node B to the mobile station UE is referred to as “a downlink” and a radio communication link used for transmitting user data from the mobile station UE to the radio base station Node B is referred to as “an uplink.”
The radio base station Node B can simultaneously perform communications with a plurality of mobile stations UE visiting one cell.
Note that, as shown in FIG. 1C, for the purpose of increasing a radio capacity, a cell controlled by the radio base station Node B is divided into a plurality of sectors by using a plurality of directional antennas (sector antennas).
Additionally, as shown in FIG. 1D, a radio resource used between the mobile station UE and the radio base station Node B is managed by a radio network controller RNC connected to the radio base station Node B through a wired transmission channel.
Note that the radio network controller RNC is normally configured to centrally control a plurality of radio base stations Node B.
By using FIG. 2, a description will be given of an uplink radio resource in a mobile communication system where CDMA (Code Division Multiple Access) is used for a radio access method.
In uplinks in the above communication system, each of a plurality of mobile stations UE, after applying encoding and modulation processes to uplink user data, transmits the user data by spreading the data into the same wide frequency range by using a spread code specific to each of the mobile stations UE.
On the other hand, after performing despreading on the uplink user data by using a spread code specific to each of the mobile stations UE upon receipt of radio signals relating to the data, the radio base station Node B decodes the data from the respective mobile stations UE by applying filtering, demodulation and decoding processes to the data.
In this case, with a signal from an intended mobile station, signals from the other mobile stations transmitting uplink user data become interference signals.
Therefore, if there are too many of other mobile stations transmitting the uplink data, or if an uplink transmission rate of the other mobile stations is too high (that is, uplink transmission power thereof is too high), the radio base station Node B is disabled to correctly decode the uplink user data of the intended mobile station.
Therefore, in the uplinks in the above mobile communication system, total received power (total interference power) in the radio base station Node B becomes “an uplink radio resource” shared by the plurality of mobile stations UE.
Here, in the case where the cell controlled by the radio base station Node B is divided into the plurality of sectors, since directivity is provided to each of the sectors, uplink radio resources (uplink interference power) shared by mobile stations UE are independent from one another between the respective sectors.
Therefore, the amount of the uplink radio resources (the uplink interference power) in the cell controlled by the radio base station Node B increases with increasing the number of the sectors (in other words, a radio capacity increases with increasing the number of the sectors).
By using FIGS. 3A to 3E, a description will be given of transmission power control and “other-cell (other-sector) interference” in the mobile communication system to which CDMA (Code Division Multiple Access) is applied.
As described above, in the above mobile communication system, total interference power in the radio base station Node B becomes a radio resource shared by a plurality of the mobile stations UE.
Therefore, the radio base station Node B controls the transmission power of the respective mobile stations UE, so that the received power is equal to minimum received power required to satisfy uplink communication quality between the radio base station Node B and each of the mobile stations UE.
In this case, the minimum received power required to satisfy uplink communication quality (hereinafter, referred to as required received power of radio base station) mainly depends on an uplink transmission rate of the mobile stations UE (i.e., a transmission rate of uplink user data) although it also changes depending on transmission environment and on moving speed of the mobile stations UE.
Here, the required received power of radio base station changes in proportion to the uplink transmission rate of the mobile station UE, and as shown in FIG. 3A, twice as much as the required received power of radio base station is needed if the uplink transmission rate becomes double.
To the contrary, if the uplink transmission rate is unchanged, the required received power of radio base station is unchanged regardless of a location of the mobile station UE visiting a particular cell (sector).
On the other hand, power of a radio signal attenuates with increasing distance through which data is transmitted. Therefore, as shown in FIGS. 3B and 3C, the radio base station Node B is configured to control, even when an uplink transmission rate of the mobile station UE is constant, transmission power of each of the mobile stations UE in the following manner.
The radio base station Node B reduces the “transmission power in mobile station” if the mobile station UE is near the base station Node B, and rises the “transmission power in mobile station” if the mobile station UE is far from the base station Node B.
However, since a transmission antenna of the mobile station UE does not have directivity, uplink transmission from the mobile station UE reaches not only a sector of the radio base station Node B to which the mobile station UE is connected through an uplink, but also another sector of the same radio base station Node B or a cell of a neighboring radio base station Node B, becomes interference in those cells (sectors).
The thus described interference caused in a neighboring cell (sector) by the transmission power from the mobile station UE will be referred to as “other-cell (other-sector) interference” (refer to FIGS. 3D and 3E).
By using FIG. 4, a description will be given of a conventional uplink radio resource control method in the mobile radio communication system to which CDMA (Code Division Multiple Access) is applied.
Conventionally, a radio network controller RNC has been performing a call admission control process and an uplink transmission rate allocation process with respect to each mobile station UE.
By referring to both transmission power, transmitter performance, a transmission rate required by an application thereof and the like of a mobile station UE requesting a connection via a dedicated channel (DCH), the radio network controller RNC accepts a connection request from the mobile station UE and determines an uplink transmission rate allocated to the mobile station UE in a range such that total interference power in a cell (sector) to which an uplink is intended to be set up and in neighboring cells (sectors) thereof respectively does not exceed maximum allowable interference power.
Subsequently, through a layer-3 (RRC: Radio Resource Control) message, the radio network controller RNC notifies the radio base station Node B and the mobile station UE of acceptance of the connection request from the mobile station UE, and of the uplink transmission rate.
Specifically, the radio network controller RNC allocates an uplink transmission rate to a mobile station UE requesting a connection via a DCH in the following manners.
(1) If the radio network controller RNC judges that total interference power in a cell (sector) to which an uplink is intended to be set up and in neighboring cells (sectors) thereof does not exceed the maximum allowable interference power respectively, it accepts a connection request from the mobile station UE, and allocates an intended uplink transmission rate.
(2) If the radio network controller RNC judges that total interference power in at least any one of a cell (sector) to which an uplink is intended to be set up and in neighboring cells (sectors) thereof exceeds the maximum allowable interference power respectively, it accepts a connection request from the mobile station UE. However, it allocates an uplink transmission rate which is lower than an intended uplink transmission rate and which is in a range such that total interference power in the cell (sector) to which the uplink is intended to be set up and in the neighboring cells (sectors) thereof do not exceed the maximum allowable interference power respectively.
(3) If the radio network controller RNC judges that total interference power in at least any one of a cell (sector) to which an uplink is intended to be set up and in neighboring cells (sectors) exceeds the maximum allowable interference power, it accepts a connection request from the mobile station UE. However, by lowering an uplink transmission rate allocated to another mobile station in the cell (sector) to which the uplink is intended to be set up or in neighboring cells (sectors) thereof, it allocates an uplink transmission rate in a range such that total interference power in the cell (sector) to which an uplink is intended to be set up and in the neighboring cells (sectors) thereof does not exceed the maximum allowable interference power respectively.
(4) If the radio network controller RNC judges that total interference power in at least any one of a cell (sector) to which an uplink is intended to be set up and neighboring cells (sectors) thereof exceeds the maximum allowable interference power respectively, it performs both controls of (2) and (3).
(5) If the radio network controller RNC judges that total interference power in at least any one of a cell (sector) to which an uplink is intended to be set up and in neighboring cells (sectors) thereof exceeds the maximum allowable interference power respectively, it does not accept a connection request from the mobile station UE.
Thus, since the radio network controller RNC normally centrally controls a large number of radio base stations Node B, it can efficiently allocate, by referring to uplink transmission states of mobile stations UE communicating with the respective radio base stations Node B, and also by referring to other-cell (other-sector) interference in the respective radio base stations Node B, uplink radio resources among mobile stations UE requesting connections to the radio base stations Node B.
By using FIGS. 5A to 5C, a description will be given of problems in the case where the radio network controller RNC performs radio resource control on an uplink in a conventional mobile radio communication system to which CDMA (Code Division Multiple Access) is applied.
Generally, in data communications, traffic often arises in a bursting manner as compared with voice communications and TV communications. Therefore, naturally, it is desired that a channel transmission rate used for data communications be changed to a high speed.
However, as shown in FIGS. 5A to 5C, the radio network controller RNC normally centrally controls a large number of radio base stations Node B, and therefore, in the conventional communication system, for reasons such as processing loads and processing delays, there has been a problem that it is difficult for the radio network controller RNC to perform alteration control on a transmission rate of a high-speed channel (in a range approximately of 1 to 100 ms).
Additionally, in the conventional communication system, even if the radio network controller RNC can perform the alteration control on the transmission rate of a high-speed channel (in a range approximately of 1 to 100 ms), there has been a problem that an equipment installation cost and a network operating cost become considerably high.
Therefore, in the conventional communication system, it is a common practice that the radio network controller RNC performs alteration control of a transmission rate of the channel in the order of several hundred milliseconds to several seconds.
Accordingly, in the conventional communication system, in a case where data transmission in a bursting manner is performed as shown in FIG. 5A, the data transmission is performed by any one of ways respectively shown in FIGS. 5B and 5C.
In FIG. 5B, the data transmission is performed by allowing a low speed, a high delay and a low transmission efficiency, and in FIG. 5C, the data transmission is performed by securing a radio resource for a high-speed communication and thus by allowing a radio bandwidth resource in a vacant time and a hardware resource in a radio base station Node B to be wasted.
Consequently, in “3GPP” and “3GPP2” which are international standardization organizations for a 3rd Generation Mobile Communication System, high-speed radio resource control methods in a layer-l between a radio base station Node B and a mobile station UE, and in a MAC sub-layer (a layer-2) have been studied for the purpose of making efficient use of a radio resource.
Hereinafter, the study itself and functions studied therein are collectively referred to as “enhanced uplink (EUL)”.
By using FIGS. 6A to 6B, a description will be given of a difference between “a radio resource control process according to a conventional method” and “a radio resource control process according to an EUL method” in an uplink in a mobile radio communication system to which CDMA (Code Division Multiple Access) is applied.
In the EUL method, in contrast to the conventional method where the radio resource control process is performed by a radio network controller RNC, the radio resource control process is configured to be performed directly by radio base stations Node B.
In the EUL method, the maximum allowable interference power in cells (sectors) are notified to the respective radio base stations Node B by the radio network controller RNC.
Then, the radio base station Node B instantly determines uplink transmission rates of respective mobile stations UE in a range such that total interference power in the cell does not exceed the maximum allowable reference power notified by the radio network controller RNC, by referring to transmission power, transmitter performance of the mobile stations UE, transmission rates needed by applications thereof and the like of the mobile stations UE connected to its own cell (sectors) through E-DCH.
Subsequently, the radio base station Node B notifies the determined uplink transmission rates to each of the mobile stations UE as a layer-1 or MAC sub-layer massage.
In the above manner, the radio base station Node B accepts connection requests of the mobile stations UE, and determines the uplink transmission rates allocated to the mobile stations UE (refer to FIGS. 6A and 6B).
Consequently, the uplink transmission rates of the mobile stations UE can be dynamically controlled into high speeds (in a range of 2 to 10 ms, for example), whereby it becomes possible to make efficient use of the uplink radio resource.
By using FIG. 7, a description will be given of problems in the EUL method where radio resource control is performed directly by a radio base station Node B.
In the EUL method, because the radio resource control is performed directly by the radio base station Node B, there arises a problem that an uplink radio resource cannot be allocated by, as is performed in the conventional method, referring to uplink transmission states and other-cell (other-sector) interference of mobile stations UE communicating with neighboring radio base stations Node B.
Consequently, if the radio base station Node B is aware only of constantly making efficient use of a radio resource in its own cell (sectors) and of satisfying desired transmission rates of mobile stations UE connected through E-DCH to its own cell (sectors), it results in causing a great deal of other-cell (other-sector) interference in the neighboring radio base stations Node B.
In this case, a transmission rate of each of the mobile stations UE connected to one of the neighboring radio base stations Node B is restricted, and hence, required communication quality therebetween cannot be satisfied. It is considered that, at worst, a call from the mobile station UE is disconnected.
As described above, in the EUL method, an uplink transmission rate of a mobile station UE can be dynamically controlled into a high speed (in a range of 2 to 10 ms, for example) by having uplink radio resource control performed directly by the radio base station Node B.
However, by having the uplink radio resource control performed directly by the radio base station Node B, there arises a problem that an uplink radio resource cannot be allocated by, as is performed in the conventional method, referring to both uplink transmission states and other-cell (other-sector) interference of mobile stations UE communicating with the neighboring radio base stations Node B.